Low Infection Type

Environmental Variability

Origin

T. monococcum accessions, including Einkorn C.I.2433 which was adopted by Stakman et al. (1962) as a pathotype differential (The, 1973a). A gene with identical specificity in chromosome 1D of T. tauschii (McIntosh, 1981) is sometimes referred to as SrX (D The, unpublished 1992).

Pathogenic Variability

Polymorphism occurs in most geographic areas. The frequencies of virulence in North America (Roelfs and McVey, 1979) and South America (Huerta-Espino, 1992) are very high compared to other regions. Virulent mutants have been detected in Australian field surveys but none has become established as a common field pathotype (Zwer et al., 1992).

Use in Agriculture

This gene has potential for limited use in areas with low frequencies of virulence if deployed together with other genes. If used alone, rapid increases in the frequency of virulent pathotypes can be anticipated. In addition, current lines with Sr21 are not adequately resistant to avirulent pathotypes as adult plants. The et al. (1988) showed that, in the absence of disease, a number of backcross-derived lines possessing Sr21 gave significantly lower yields than near-isogenic counterparts that did not carry the gene.

Observed on stem rust differentials for six races of Puccinia graminis f. sp. tritici in the Ug99 race group identified from samples collected in Kenya during 2008 to 2014.
Infection types (IT) observed on seedlings at 14 days postinoculation using a 0-to-4 scale according to Stakman et al. (1962), where IT of 0, ;, 1, 2, or combinations thereof are considered to be a low IT and IT of 3 or higher are considered to be a high IT.

Related Literature

Detection of Wheat Stem Rust Races TTHSK and PTKTK in the Ug99 Race Group in Kenya in 2014
Plant Disease · 2016
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